1. Field of the Invention
The present invention relates to an internal combustion engine. More particularly, the present invention relates to a lubrication system for a four-cycle vertically-oriented engine.
2. Description of the Related Art
Internal combustion engines operating on a four-cycle principle may be provided with a pressure lubricating system for lubricating various engine components. Internal combustion engines that are used to power watercraft featuring outboard motors are commonly vertically oriented within a cowling of the motor. In this arrangement, each piston reciprocates along a generally horizontal axis. Also, a crankshaft and each camshaft typically rotates about a substantially vertical axis.
In such arrangements, lubricating the shafts poses a number of problems specific to vertically-oriented watercraft engines. For instance, due to the vertical arrangement of the shafts, lubricant must be supplied at an upper point of each shaft such that it can drain downward to lubricate the shaft and each of the bearings along its length. The lubricant would then pool within a bottom portion of each chamber housing a shaft. To facilitate recirculation and avoid flood the chambers with lubricant, the bottom of each chamber would be connected to a lubricant reservoir or pan by a single passage. The lubricant pooling at the bottom of the chamber could then drain into the lubricant pan through this passage.
Because the lubricant pan was not sealed from a bottom side of the pistons and the cylinders, exhaust gases that blow-by the piston during the exhaust stroke of the engine would frequently pass into the lubricant pan. A difficulty arose when blow-by gases accumulating inside the oil pan streamed through the drain passages against the flow of the draining lubricant. The collision between the draining lubricant and the blow-by gases inhibited a smooth flow of the lubricant out of the chambers. Frequently, the inhibition of lubricant flow caused flooding of the chambers and excessive entrainment of lubricant within the blow-by gases.
One method envisioned to solve this problem involved enlarging a cross-sectional area of the passage such that both the blow-by gases and the lubricant could flow uninhibited. However, in order to accommodate such an enlarged passage, the cylinder block containing the enlarged passage had to be enlarged as well. Such an enlargement disadvantageously increases the weight of the outboard motor. Alternatively, two separate passages were formed within the cylinder block such that lubricant may pass through one passage while blow-by gases could pass through the other. However, this arrangement also results in disadvantageously increasing the cylinder block size to accommodate the internal passageways. Moreover, expenses associated with manufacturing the cylinder block increased due to the increase in cylinder block geometry.
Accordingly, an efficient and cost-effective method of venting the blow-by gases from the lubrication pan is desired. Additionally, a structure enabling the blow-by gases to be effectively separated from the lubricant is also desired which does not result in an increased engine size.
According to one aspect of the invention an outboard motor has a four-cycle engine. The engine includes a cylinder block having at least one cylinder. The cylinder preferably has a substantially horizontal axis. A piston is arranged for reciprocation within the cylinder and is connected to an output shaft. The output shaft preferably has a substantially vertical axis. The engine also includes a head assembly connected to the cylinder block. Moreover, the engine further comprises at least one combustion chamber that is defined between the head assembly and a piston. There are at least one intake port and at least one exhaust port arranged to communicate with the combustion chamber. The engine also has an intake valve capable of closing and opening the intake port and an exhaust valve capable of closing and opening the exhaust port. An intake cam shaft is configured to be capable of moving the intake valves while an exhaust cam shaft is configured to be capable of moving the exhaust valves. The engine also has a head cover positioned over the intake cam shaft and the exhaust cam shaft to defining, in part, a cam chamber. The engine has a lubrication reservoir arranged generally below a lower end of the cylinder block. A lubricant return passageway preferably extends between the cam chamber and the lubrication reservoir while a separate gas passageway also connects the lubrication reservoir and the cam chamber. Preferably at least a portion of the gas passageway includes a gas pipe positioned external to the engine.
According to another aspect of the present invention, an outboard motor generally comprises an engine. The engine includes a generally vertically-oriented camshaft that is contained within a camshaft chamber. The engine also has a lubricant reservoir with a lubricant pump arranged to pump lubricant from the lubricant reservoir to at least one location proximate the camshaft. A lubricant return passage extends between a lower portion of the camshaft chamber and the lubricant reservoir while a gas passage extends between the lubricant reservoir and the camshaft chamber. The gas passage preferably enters the camshaft chamber at a location that is vertically higher than an opening in the camshaft chamber leading to the lubricant return passage and preferably at least a portion of the gas passage is external to the engine.